Orthogonal Frequency Division Multiplexing (OFDM) is the basis for several wireless standards such as IEEE 802.11a, IEEE 802.11g, IEEE P802.15.3, IEEE 802.20 and IEEE 802.16. These standards are utilized in many portable and handheld computer devices such as laptop PC, Personal Digital Assistances, multimedia viewers (e.g., for use with DVB, and DVB-H networks) and cellular telephones. A traditional heterodyne receiver can be utilized to receive OFDM based signals. However, the integration of a traditional receiver onto a single integrated circuit is complex and expensive. Additionally, a single chip heterodyne system typically uses higher levels of electrical power to operate. In the portable device market, the efficiency and duration of the power supply system is an important aspect of device performance. Thus, a heterodyne system on a chip is not a preferable solution for portable devices.
An alternative to a traditional heterodyne receiver is the Zero Intermediate Frequency (ZIF) direct-conversion receiver. A ZIF direct-conversion receiver is generally easier to manufacture as a single integrated circuit, and therefore provides improved power consumption performance as compared to a traditional heterodyne receiver. A design issue associated with the ZIF direct-conversion receiver is the potential signal degradation due to an imbalance between the In-phase (I) and Quadrature-phase (Q) branches in the baseband signal. In general, an I/Q imbalance is caused by a mismatching of analog components within the receiver (e.g., doping concentration and oxide thickness in CMOS circuits). The imbalance is likely to increase with higher silicon integration, as well as higher carrier frequencies.
Some useful I/Q imbalance compensation algorithms are available. These algorithms, however, generally require complex circuit elements to handle functions such as special training performance of the receiver.